This invention relates to a joint structure including ball joints for use in foldable baby carriages.
This invention is applicable, for example, to a baby carriage of basic foldable construction as disclosed in Japanese Patent Publication No. 50705/1982 (which substantially corresponds to U.S. Pat. No. 4,317,581) filed by the same applicant as in this application. The baby carriage disclosed in said publication is so designed that its dimensions in three directions, height, length and width, are decreased when the baby carriage changes from its opened to its closed state. Folding movements taking place in these directions are operatively associated with each other.
When such foldable baby carriage is observed, it is seen that the movements of some components taking place during folding operation are not confined to a single plane but require a three-dimensional space. For example, there is a case where if a joint which allows rotation only about a signal axis is used between one component and another connected thereto, the use of said joint is found insufficient; rather, a so-called universal joint which allows rotation around a first axis and rotation around a second axis which intersects the first axis at a predetermined angle is required. As a form of such universal joint, a ball joint may be considered.
A ball joint can be used as a joint portion which allows rotation around a first axis and rotation around a second axis, as described above. If, however, such ball joint, which allows rotation around axes extending in almost all directions, is used in a foldable baby carriage, there would be a case where contrarily it interferes with the opening and closing operation of the baby carriage. Thus, even if a ball joint is to be used in a foldable baby carriage, it would bring about better results to allow only the necessary movements to take place in the opening and closing operation of the baby carriages.
Usually, a ball joint must be so assembled that a ball received in a socket to form a ball articulation will not come off the socket. Attainment of such assembly, however, entails the use of complicated parts, and the assembly operation itself is often complicated.